1. Field of the Invention
This invention relates to light measuring devices in which the light measurement is automatically performed on a heat source in the image frame of camera by using an infrared ray sensor.
2. Description of the Prior Art
In the situation where an object most desirable to photograph (for example, a person) lies at the marginal portion of the image frame, with general cameras, there is a possibility for that object to be improperly exposed, for example, under-exposed. The reason for this is that the light measuring function of the general camera employs the average light measuring method.
To eliminate such a problem, another method for measuring light from only a particular portion of the photographic picture frame, for example, the abovementioned person, or so-called spot light measuring method, has been proposed, and, at the present time, is employed in various cameras.
However, in order for an object, situated such that an under-exposure will result as has been described above to be photographed at a proper exposure by this spot light measuring method, the photographer must first preliminarily position that object at the center of the image frame for performing the light measurement, and then after the result of this light measurement has been memorized, determine a composition so that the object intended to be photographed is brought back to the desired position of the image frame, for example, in the marginal portion. For this reason, there has been a drawback that the management to snap shots became bad because the above-described preliminary operation was necessary from the light measurement on the object until the exposure.
Also, there is a known method that the individual portions of the photographic image frame are made selectively possible for light measurement and, even in the above-described situation, the light from the object positioned in the marginal portion of the image frame can be measured while fixing the photographic image frame. Even in this method, the photographer must choose the appropriate light measuring output of the light measuring circuit which is measuring the light of the photographic object portion. So there remains a possibility of not choosing the output accurately.